1. Field of the Invention
The present invention relates to a rear conversion lens system, and more particularly relates to such rear conversion system which can change the focal length of the whole lens system by attaching or detaching it between the main lens system and the image plane.
2. Description of the Prior Art
In recent years, the lens system for the dual-focus camera having a main lens system and a rear conversion lens system has been proposed in the lens shutter camera design. In this system, only a main lens system operates as a photographic lens in a standard focal length condition, while the main lens system is shifted frontward along the optical axis and a rear conversion lens system is inserted behind the main lens system in a telephoto focal length condition.
At present, however, it is hard to say that a sufficient variable ratio has been obtained in the rear conversion lens system. For example, in the Japanese Patent Laid-Open No. 42513/1984, the rear conversion system is constituted with two groups comprising three lenses, but the variable ratio is about 1.5.